1. Field of the Invention
This invention relates to a method of forming a contact via during a metallization process, which avoids contamination of the filling metal.
2. Description of the Related Art
A contact via can be used to connect two different conductive layers together, for example, two metal layers, in an IC (Integrated Circuit) device. The conventional procedure includes forming an inter-metal dielectric (IMD) layer above a first conductive layer. The IMD layer is selectively etched to form the contact via and to expose the first conductive layer. Metal is provided to fill the contact via forming a plug. Finally, a second conductive layer is formed above the IMD layer.
Typically, the IMD layer includes one first insulation layer, one spin-on glass (SOG) layer, and one second insulation layer. However, the SOG layer may lead to the occurrence of an out-gassing phenomenon, due to the generation of moisture after performing an O.sub.2 plasma treatment. The out-gassing phenomenon may cause the metal, for example, the aluminum alloy, which fills the contact via to become contaminated. The contaminated metal will have a high resistance, thus adversely affecting the performance of the IC device. Many methods have been proposed to rectify this problem, such as a partial-etch-back (PEB) method proposed by Intel U. S, and an ion implantation method proposed by UMC Taiwan, etc. The ion implantation method may eliminate the problem of contaminated metal, but it may also simultaneously change the structure of the SOG layer.
FIG. 1A is a representation of the atomic structure of the SOG layer. The SOG layer is comprised of siloxane. As shown in FIG. 1B, arsenic (As) ions are implanted using physically-forced replacement of the bond between the silicon atom and the organic function group R, for example, an alkyl group (CH.sub.3) or a phenyl group (C.sub.6 H.sub.5). The function group bonding causes the SOG layer to have a low dielectric constant. However, after implanting of the arsenic ions, the new bonding structure disadvantageously raises the dielectric constant; thus, the original characteristic of a low dielectric constant of the SOG layer is lost.